The present intention relates to an iron-based sintered alloy which is wear-resistant at high temperature. Such sintered alloy is preferably used as a material for mechanical parts (e.g., such as valve seat insert used in internal combustion engine) that require wear resistance at high temperature.
Japanese Patent Examined Publication JP-B-5-55593 and Japanese Patent Unexamined Publication JP-A-7-233454 disclose high-temperature wear-resistant sintered alloys each being high in cobalt content. However, the production cost of these sintered alloys is high, due to the use of relatively large amounts of cobalt.
JP-A-5-9667 discloses an iron-based sintered alloy containing an iron-based matrix and an ironbased hard phase dispersed in the matrix. The hard phase contains C, Cr, Mo, W, V, Si, and Mn. JP-B-1-51539 discloses an iron-based sintered alloy containing an iron-based matrix and a dispersed phase containing Cr, C, Mo, Si, and at least one selected from Nb, Ta, Ti and V. According to these patent publications ""667 and ""539, however, it is difficult to prepare a sintered alloy that is superior in wear resistance and at the same time is weak in the property of damaging another member that is in contact with the sintered alloy
U.S. Pat. No. 5,949,003, corresponding to JP-A-10-310861, discloses a high-temperature wear-resistant sintered alloy.
It is an object of the present invention to provide a sintered alloy that is greatly improved in wear resistance at high temperature and compatibility, while suppressing damage to mating part that is in contact with the sintered alloy.
According to a first aspect of the present invention, there is provided a first high-temperature wear-resistant sintered alloy. This sintered alloy comprises, based on a total weight of the sintered alloy, 3.74-13.36 wt % of W, 0.39-5.58 wt % of V, 0.2-5.78 wt % of Cr, 0.1-0.6 wt % of Si, 0.39-1.99 wt % of Mn, 0.21-1.18 wt % of S, up to 2.16 wt % of C, and a balance consisting of Fe and inevitable impurity. The sintered alloy includes a first phase comprising, based on a total weight of the first phase, 3-7 wt % of W, up to 1 wt % of Cr, 0.1-0.6 wt % of Si, 0.2-1 wt % of Mn, 0.1-0.6 wt % of S, up to 2.2 wt % of C, and a balance consisting of Fe and inevitable impurity. This first phase may further comprises 0.5-1.5 wt % of V. The sintered alloy further includes a second phase comprising, based on a total weight of the second phase, 7-15 wt % of W, 2-7 wt % of V, 1-7 wt % of Cr, 0.1-0.6 wt % of Si, 0.2-1 wt % of Mn. 0.1-0.6 wt % of S, up to 2.2 wt % of C, and a balance consisting of Fe and inevitable impurity. 0.3-1.6 wt % of first MnS grains, based on the total weight of the first phase, and first carbides of at least tungsten are dispersed in the first phase. The first carbides have fine particles. 0.3-1.6 wt % of second MnS grains, based on the total weight of the second phase, and second carbides of at least tungsten are dispersed in the second phase. The second carbides include tungsten carbides having a particle diameter of at least 1 xcexcm and is in an amount of 10-20 areal %, based on a total area of the second phase. The first phases are in an amount of from 20 to 80 wt %, based on a total weight of the first and second phases. The first and second phases are distributed in the sintered alloy, in a form of spots. 0.3-1.6 wt % of third MnS grains, based on the total weight of the sintered alloy, are dispersed in boundaries surrounding grains of said first and second phases and/or in pores of the sintered alloy.
According to a second aspect of the present invention, there is provided a second high-temperature wear-resistant sintered alloy that is identical with the first sintered alloy, except that the vanadium content of the sintered alloy is 0.79-5.88 wt %, in place of 0.39-5.68 wt %, based on the total weight of the sintered alloy, and that the first phase further comprises 0.5-1.5 wt % of V, based on the total weight of the first phase.
It is needless to say that each of the first and second sintered alloys may contain inevitable impurities.